F

FDM
Frequency Division Multiplexing. Combining signals at differing frequencies such that they can subsequently be separated by filtering at the receiver.

FEC
Forward Error Correction. Encoding data prior to sending so that errors can be detected and corrected by the receiver. FEC coding schemes allow receivers to reliably discriminate signals from high noise levels.

Feedhorn
The aperture antenna that is used to introduce microwave radiation into the satellite antenna.

Filter
A device that separates signals based on their frequency. A high pass filter will attenuate low frequencies and pass higher ones, a Low pass filter does the opposite, and a bandpass filter will pass only a selected range of frequencies.

Firewall
A system through which all traffic into a sub-network must pass to reach other sub-networks. The firewall ensures only authorised users gain access from outside networks.

FM
Frequency Modulation; a method for modifying the frequency of a carrier to represent the information to be sent. Commonly used in audio systems.

Footprint
Map of the coverage area of a satellite

Frame Relay
A fast packet switched technology used in public networks.

FSS
The Fixed Satellite Service, pertaining to permanently installed earth stations / terminals.

ftp
File Transfer Protocol, a basic application used to exchange files reliably over an IP network such as the Internet.

Full-duplex
A system that can, at once, send and receive information.